patch 9.1.0284: make testclean is not able to delete failed screendumps

Problem:  make testclean is not able to delete failed screendumps.
Solution: Remove the "failed" directory when necessary.
          (Julio B)

Patch 8.1.1080 changed the way that failed screendumps are saved, but
the "rm -rf *.failed" clean command was not ported correctly.

closes: #14468

Signed-off-by: Julio B <julio.bacel@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index dc9f775..bafbe5b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    284,
+/**/
     283,
 /**/
     282,